Thirteen of the warmest years recorded have occurred within the last decade and a half, proving that global warming is a reality, the UN's World Meteorological Organization (WMO) said on Tuesday.

The year 2011 caps a decade that ties the record as the hottest ever measured, the WMO said in a provisional report on climate trends and extreme weather events, unveiled at UN climate talks in Durban.

"Our science is solid and it proves unequivocally that the world is warming and that this warming is due to human activities," WMO Secretary-General Michel Jarraud said in a statement, adding that policy makers should take note of the findings.

"Concentrations of greenhouse gases in the atmosphere have reached new highs and are very rapidly approaching levels consistent with a 2 to 2.4 Celsius rise in average global temperatures."

Scientists believe that any rise above the 2.0 threshold could trigger far-reaching and irreversible changes over land and in the seas.

The 2002-2011 period equals 2001-2010 as the warmest decade since 1850, the report said.

2011 ranks as the 10th warmest year since 1850, when accurate measurements began.

This was true despite a cooling La Nina event - one of the strongest in 60 years - that developed in the tropical Pacific in the second half of 2010 and continued until May 2011.

The report noted that the cyclical climate phenomenon, which strikes every three to seven years, helped drive extreme weather events including drought in east Africa, islands in the equatorial Pacific and the southern United States.

A separate report also released Tuesday showed that Pakistan, Guatemala and Colombia were the countries worst hit in 2010 by extreme weather events.

Over a 20-year span, Bangladesh, Myanmar and Honduras were shown to be most vulnerable to Nature's violent outbursts, said the report by European NGO Germanwatch. Vietnam ranked sixth among the countries most affected by climate change from 1991 to 2010, the report said.